Almost certainly 26.4 (Cinelli standard so needs Cinelli bars) and I wouldn;t recommend using 26.0 bars beacuase the wedge that holds them in place will put a fair bit of pressure on a small par of the bars. BTW, it's missing the plastic Cinelli logo bit that should go in the hole on the front, if that matters to anyone.
Almost certainly 26.4 (Cinelli standard so needs Cinelli bars) and I wouldn;t recommend using 26.0 bars beacuase the wedge that holds them in place will put a fair bit of pressure on a small par of the bars. BTW, it's missing the plastic Cinelli logo bit that should go in the hole on the front, if that matters to anyone.